This is an improved process for drying a cellulose ester membrane.
It is well known in the art that water-wet membranes are first advantageously dried to afford the best properties for the separation of gaseous mixtures. Numerous techniques for drying water-wet membranes, while minimizing adverse effects on the membrane properties, are taught in the prior art. U.S. Pat. No. 3,842,515 teaches the sequential treatment of a water-wet, cellulose acetate membrane with a non-polar organic liquid at less than ambient temperatures. It is disclosed therein that the solvents can be introduced into the bores of hollow fibers. U.S. Pat. No. 4,068,387 teaches that the membrane can be dried by treatment with a volatile aliphatic hydrocarbon having specific solubility parameters. Optionally, it is disclosed in column 4 that the solvents can be pumped through the bores of hollow fibers. U.S. Pat. No. 4,080,743 discloses the immersion of a water-wet membrane in a mixture of water-miscible and immiscible liquids followed by drying in an air stream. U.S. Pat. No. 4,080,744 teaches the treatment of a membrane with a solvent which cannot dissolve all of the water present in the membrane. U.S. Pat. No. 4,127,625 describes the treatment of the membrane with a solution of salt followed by freeze drying.
In general, the aforementioned processes for drying membranes have been time-consuming and yielded membranes having variable permeabilities. Accordingly, a more rapid and predictable process for drying water-wet membranes would be advantageous.